Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is in an ink jet printer. As the fluid droplet size and speed of fluid ejection increases, factors that effect fluid ejection are magnified requiring solutions to problems that previously did not exist.
Micro-fluid ejection devices, such as ink jet printers, with replaceable fluid supply tanks may have or develop a problem of trapping air adjacent to a connection between the fluid supply tank and an ejection head structure. Trapped air may also be confined in an intermediate area between a fluid flow path from the fluid supply in a cartridge or tank and the ejection head structure. Expansion and/or contraction of the trapped air as the result of atmospheric pressure or altitude changes may result in changes in pressure of the fluid at nozzles in the ejection head. Such pressure changes or air expansion may result in seepage of fluid from the nozzles when the nozzles are exposed to less than atmospheric pressure or air intake into the nozzles when there is a negative pressure in the ejection head adjacent to the nozzles.
When the fluid supply container is removably attached to a permanent or semi-permanent ejection head structure, there are additional concerns with regard to trapping air. Typically, during the attachment or removal of a fluid supply tank onto a permanent or semi-permanent micro-fluid ejection head, there may be an air space or volume of air in an exit port of the fluid supply tank and/or flow features in the ejection head. A change in air volume may result from the displacements encountered in the process of exchanging fluid supply tanks and such volume change may cause seepage of fluid from the ejection head nozzles or air ingestion at the nozzles. For proper or prolonged operation of the ejection head, it is desirable to avoid both of these situations.
In a multi-fluid supply tank having ejection heads that eject multiple different fluids, such as different colored inks, for example, seepage of fluid from the nozzles may result in cross-contamination of fluids. Some fluid containers include a relatively large breathing mechanism (a spring loaded air bag within the tank, for example) and relatively large air storage volumes to retain and accommodate ingested air and volume changes due to pressure changes. In other instances, a purging pump may be used to remove air through the nozzles of the ejection head. When a purging pump is used, the ejection head is moved to a maintenance station where purging of air may occur.
The removal of air from the fluid storage tanks becomes even more critical as the size of the storage tanks is decreased relative to an amount of fluid contained in the storage tank. In larger fluid storage tanks, an excess volume is available for reducing the effects of air volume changes in the tank. However, smaller tanks having the same volume of fluid as larger tanks are less tolerant of air volume changes. Also, it is not desirable, from a cost point of view, to provide an air purging pump system to remove air from the fluid storage tanks. Accordingly, there is a need for a more cost effective device to remove air from fluid storage tanks for micro-fluid ejection devices.
In view of the foregoing needs, one embodiment of the disclosure provides a fluid supply tank for a micro-fluid ejection head. The fluid supply tank has a body portion for holding a fluid to be ejected. The body portion includes a fluid exit port on an exit end thereof and a cover on an opposing end thereof. An internal vent conduit is disposed in the tank between the exit end and the cover for air removal adjacent the exit port.
Another embodiment of the disclosure provides a method for enhancing the operation of a micro-fluid ejection device. The method includes, disposing an internal vent conduit in a fluid supply container for the micro-fluid ejection device. The vent conduit is disposed between a fluid exit end of the container and a container cover opposite the fluid exit end. The fluid supply container is installed on the micro-fluid ejection device so that any trapped air between the container and the device is urged through the internal vent conduit through an atmospheric vent in the cover.
The exemplary embodiments disclosed herein may mitigate the above described problems by providing a vent path in an interior portion of the fluid supply tank between the cover and the fluid exit port of the fluid supply tank. The vent may be effective for venting air adjacent the outlet port when the outlet port is sealed, in the case of a removable fluid supply tank or may be effective to remove air from fluid supply paths in an ejection head for a disposable fluid supply tank and ejection head. Removal of air is important to prevent unwanted or untimely loss of fluid from the fluid storage tank as a result of atmospheric pressure changes that may expand or contract any air bubbles inside the tank.
Exemplary embodiments may avoid having to configure ejection head tanks with large air collection volumes or having to incorporate into the fluid ejection devices such as printers, air removal mechanisms or purge maintenance stations. Another advantage of the ventilation path may be that the path allows fluid to be absorbed into the felts rather than retained in the fluid exit port of the tank. Trapped air that expands adjacent to the fluid exit port may be effectively removed using the ventilation path provided in the tank.